How much capacity do you need? When you read the manufacturer's description of a toaster oven, one of the first things you'll see are what size pizza it accommodates, how many slices of bread it will toast at once, and the size of chicken it will roast. These are important guidelines because they can help you narrow down your choice by the size of the group you generally cook for, as well as the most common items you cook. For example, for a large family, a six-slice toaster oven, along with its correspondingly larger capacity is probably a must. By the same token, even if there's only two of you, if beef roasts or roast chicken are your main entrees, be sure to look for a toaster oven that's sized large enough to handle those items.
What do you plan to cook? If all you really need is something to toast bread, don't take up more counter space than you have to, just head on over to our report on toasters and that should do you fine. However, if you're a bread baker, you'll be better served with a toaster oven with a convection or steam feature; traditional toaster ovens don't perform as well for that type of baking. If you're just using your toaster oven for broiling or heating up pizzas, a toaster oven without a convection feature will be more than adequate.
How much counter space do you have? Toaster ovens come in all sizes. Know beforehand what your space limitations are, making sure to include extra room around the unit for ventilation. Check out the dimensions on the manufacturers' websites, and then take a tape measure to your counter. There are many unhappy toaster-oven owners who give a product a poor rating and say things like, "It's not as big/small as it looks in the picture." In this case, a picture is not worth a thousand words -- do the math instead.
Do you want an inexpensive convection option? We saw an astounding number of reviews from people who were wanting a convection oven, but could not afford to replace their current range or stove. Instead, they just added a toaster oven with a convection feature to their kitchen and they are very happy that they did so. While a toaster oven will be smaller than your oven, and thus not suitable for everything, it does enable you to have a convection option at a much lower price than a full-sized oven or range would cost.